A Grover. Online. Saying stuff.

Tag Archives: fedora

target-isns recently was added to Rawhide, and will be in a future Fedora release. This add-on to LIO allows it to register with an iSNS server, which potential initiators can then query for available targets. (On Fedora, see isns-utils for both the server, and client query tools.) This removes one of the few remaining areas that other target implementations have been ahead of LIO.

Gnome since 3.8 has restricted the Blank Screen time to between 1 and 15 minutes, or “Never”, to disable screen blanking/locking entirely. If this isn’t granular enough, you can set other values like so:<del datetime="2014-03-25T22:25:42+00:00">dconf write /org/gnome/desktop/session/idle-delay 1800</del>gsettings set org.gnome.desktop.session idle-delay 1800
The value is in seconds, so here we set the delay to 30 minutes (60*30=1800). It seems that once doing this, the UI will show “Never”, but the set value is still used correctly.
There is also a “Presentation Mode” shell extension that adds a button to inhibit screen lock, but for me, I still wanted to have it automatically lock, but just a little bit slower.

EDIT: dconf didn’t actually work! Apparently gsettings is the way to go.

tl;dr: Puppet/Chef make Fedora’s short support period much less of an issue.

The OS is a building block

I’ve been watching a lot of videos on DevOps lately. Several close friends of mine are sysadmins and I’ve been learning a lot from them about the transformation that their profession is undergoing. From this year’s ChefConf, Adam Jacob’s keynote and the talk by Sascha Bates really impressed on me the big change in how admins should view machines — They’re not permanent, or even semi-permanent. They are ephemeral snowflakes that may live a year, or just an hour, so don’t get too attached.

Part of why admins like VMs is because the isolation they provide between different services. I used to run mail, DNS, and httpd from a single machine. Everything was mostly separate but not quite everything. They had separate userids but everyone’s config was in /etc, even touching the same files, sometimes. A full disk affected everybody. /var/log/messages didn’t split up their logging cleanly (by default, anyway.) It all just was built assuming there would be an admin at a command shell who could use their brain to resolve the conflicts to make everything play nice on a single OS image.

One service per instance

Admins adopted VMs for isolation, increased density, and better per-service resource allocation, but then ran into other problems. The setup that they did by hand once per new-hardware now was once per instance. (Editing /etc/sudoers for the fiftieth time gets old.) The tools then evolved further, until today one may keep no persistent state in an instance. Now, an instance is kickstarted into existence and configured automatically for the one job it will ever do. The sysadmin’s job isn’t to herd boxen any more, it’s to build ’em, run ’em, and then reap ’em.

All the OS mechanisms for co-existing server processes, they’re now either obsolete or vestigial to some degree. What is important is the malleability of the OS to assume all the tasks it may be asked to – rather like a stem cell needs to be able to become a nerve or muscle, but never needs to be both.

Never upgrade, just redeploy

Let’s come back to the odd fact that Fedora is both a precursor to RHEL, and yet almost never used in production as a server OS. I think this is going to change. In a world where instances are deployed constantly, instances are born and die but the herd lives on. Once everyone has their infrastructure encoded into a configuration management system, Fedora’s short release cycle becomes much less of a burden. If I have service foo deployed on a Fedora X instance, I will never be upgrading that instance. Instead I’ll be provisioning a new Fedora X+1 instance to run the foo service, start it, and throw the old instance in the proverbial bitbucket once the new one works.

Cheap and easy virt and config management gives admins what they’ve always wanted — stability when they want it (run a LT support distro image, or for the VM host) or the latest stuff for their fast-moving business-oriented instances, by running a fast-update or rolling-release distro.

What Fedora should do

We’re already working on some of these to some degree — I think we should try to do even more to ensure Fedora is useful for the fast-update instance role.

First, Fedora needs to be able to be small. Nobody’s going to read the manpages on a throwaway instance, nobody’s even going to run vi. Image size matters when multiplied for each instance. Can we get by without /usr/share/doc/* and its thousands of copies of the GPL text? Fedora seems pretty good but there must be more we can do.

Second, we need to ensure Fedora supports the packages people are really using these days. Latest Ruby. Latest OpenStack. Vagrant. Django. Chef. Puppet. All the weird JS stuff that’s popular now on GitHub. 🙂 Continue to improve packaging tools so it’s easier for new contributors to do their first package, as well as for long-time packagers to maintain more packages. And not just package for contribution to Fedora, but for admins to package for solely internal distribution. Like Sascha Bates stresses in her talk, packaging is a huge benefit to automation, but it does require effort. It can be easier.

Finally, I think we need to continue to look at how easy it is to configure and manage an instance of the OS, and tailor it more for automated configuration. I believe the key to this is adding programmatic interfaces where they are lacking. See my “All Plumbing needs an API” talk. Since we’re probably being configured by another piece of code rather than a person at the shell, we need clear, unambiguous programmatic interfaces with good error handling. Chef should not be calling cmdline tools and checking error codes, there should be a Ruby configuration library that natively controls the whatever-it-is directly! We want configuring Fedora to be fast, straightforward, and reliable.

Conclusion: Stable+fast-update is better than stable+self-built

Practically the whole history of Linux distros has been the conflict between stability and new features. With virtualization, one still must make this choice, but at a much finer granularity than before. If you’re going to re-instance within 6 months anyways, why manually build your latest-Ruby and whatnot to support your app on top of a stable distro image? Maybe just use Fedora for those.

In addition to turning your Fedora 18 box into an iSCSI target, LIO also supports other SCSI transport layers (‘fabrics’), such as Fibre Channel, with the qla2xxx fabric.

The most crucial bit is to verify that the qla2xxx driver has initiator mode disabled — it should be operating in target mode only. You can check this with:

cat /sys/module/qla2xxx/parameters/qlini_mode

It should say ‘disabled’. If it doesn’t, create a file called /usr/lib/modprobe.d/qla2xxx.conf and put:

options qla2xxx qlini_mode=disabled

in it. Then, run ‘dracut -f’ to rebuild your initrd, and reboot.

Some of you may be wondering: why /usr/lib/modprobe.d instead of /etc/modprobe.d ? This is because qla2xxx is likely loaded from the kernel’s initial ramdisk (initrd), and dracut, the initrd building tool, omits “host-specific” settings in /etc/modprobe.d. While you’re mucking around, also make sure the firmware package for your qla device, such as ql2200-firmware or similar, is also installed.

targetcli won’t let you create a qla2xxx fabric if qlini_mode is wrong. Once it lets you create the qla fabric, you can add luns to it and grant access permissions to acls exactly in the same manner as the other LIO fabrics.

python-kmod is a basic Python wrapper around the kmod library. It allows you to load, unload, and view Linux kernel modules without resorting to the subprocess module.

If you have Python code that works with kernel modules, please consider using this library in the future. If you have C code that works with modules, you should use libkmod directly! As I’ll be talking about at this years LPC, proper libraries are preferable to calling cmdline progams for low-level stuff, and now there’s one less reason to do so.

Using python-kmod, python-rtslib (and thus targetcli and targetd) now work with no use of subprocess, although rtslib will fall back to modprobe via subprocess if python-kmod is not present.

Thanks to Jiri Popelka for reviewing the python-kmod package, sorry it took me so long to fix it up 🙂

Second, I’m having trouble implementing SSL support. I searched around and found some pages that talked about easily adding SSL support to Python’s HTTPServer, but after spending a day on it, it still didn’t work. I’m sure this is easy for someone, but that someone is not me 🙂 Anyone care to take a look?

targetd is a new service that will make it easier to configure Linux machines to export block-based volumes over iSCSI or other protocol.

The Why

Virtual machines need disk images to run from. While you can put the disk image on the local storage of the machine executing the VM, there are many benefits to centralizing disk images — this lets you seamlessly migrate the VM’s execution between machines, is easier to manage, and can be more space-efficient when many of the disk images are almost the same, which is pretty common.

However, it hasn’t been nearly as easy to provision a new storage volume on the central storage box as it could be. High-end storage appliances have tools for this, but the normal way using only open-source tools has been to ssh into the machine, create the new volume and export it using command–line tools, and then go back to however you’re creating the new VM and tell it about the new volume you created.

targetd is a step towards making this process a little easier.

The What

The remote API is based on jsonrpc-2.0 over HTTP. The Python standard library does much of the work towards implementing our API server, what’s left is the actual implementation of functionality and the jsonrpc error handling.

This API will let targetd eventually tie into existing storage management tools. One such under development is libstoragemgmt, a framework by my colleague Tony Asleson, which will give virtualization tools like oVirt or OpenStack a common API for management of the many proprietary storage appliances, and also open-source appliances like targetd.

Linux has had reliable LVM-based volume management for a long time, and now has an excellent kernel-based storage target subsystem called LIO. targetd uses both of these heavily. In configuring a machine for a storage appliance role, give targetd a volume group to allocate volumes from, set user/password for access, and you’re just about done.

There is one coding pet peeve of mine that I’ve ranted about before that targetd avoids completely. targetd uses libraries to interface with LVM and LIO instead of the all-too-common alternative of passing commands to command-line tools, and parsing the output. Much of the time spent towards targetd was improving theselibraries. I believe proper error propagation, reduced text parsing, and better library APIs make this bottom-up approach a long-term win.

Current state and future plans

Today’s announcement is a pre-alpha 0.1 release. I’m really hoping to get to 1.0 for Fedora 18. There is a manpage to write and SSL support to add, but much more important than the source code of targetd is the layout of the remote API itself. I’d love to get some more review of that, as well as the code, before 1.0. I have been working from what I believe are some common use-cases, but more feedback on how admins configure and use storage appliances would be most welcome too!

Gnome 3 has the option of disabling the trackpad while the user is typing. (System Settings -> Mouse and Touchpad -> Touchpad) However, it uses a timeout of two seconds. Two seconds doesn’t sound like much, but it may be enough to feel weird — at least it did for me.

When you check that option, all Gnome is doing is running a utility called “syndaemon”, and it uses a 2 second timeout. We can adjust the timeout by running this ourselves when we login:

Make sure Gnome doesn’t also run syndaemon by keeping the aforementioned checkbox unchecked

Run gnome-session-properties, after entering alt-F2 or from the commandline.

Click Add, and then enter Syndaemon, /usr/bin/syndaemon -i 0.5 -K -R, and any comment you want

Click Save.

Logout and back in

If you run “ps ax|grep synd” you will see syndaemon has been started with your settings. 0.5 seconds works for me but feel free to experiment.